Boundary layer wind turbine with tangential rotor blades

ABSTRACT

A wind turbine having rotor assembly with a plurality of stacked disks ( 1 ) for rotation about an axis. At least one set of the stacked disks has disks being closely spaced from each other for creating a boundary layer effect on surfaces of the disks that contributes in rotating the disks. Each disk has a plurality of rotor blades ( 2 ) disposed on an outer circumference thereof. Each rotor blade ( 2 ) has at least one surface extending tangentially from the outer circumference of each disk ( 1 ) for redirecting the airflow tangentially to a peripheral surface of each disk ( 1 ). Each disk ( 1 ) defines at least one opening ( 4 ) thereon for redirecting the wind axially through each of the disks ( 1 ).

FIELD OF THE INVENTION

The present invention relates to wind turbines used to convert windenergy into mechanical energy, more specifically to wind turbines thatuses the phenomenon of boundary layer on a surface to extract the windenergy.

BACKGROUND OF THE INVENTION

Wind as a source of energy is a concept that has been promoted fromancient time. According to historical sources, there is evidence whichshows that windmills were in use in Babylon and in China as early as2000 B.C.

Wind is used as a source of energy for driving horizontal axis andvertical axis windmills. Horizontal axis windmills have been usedextensively to drive electrical generators, however they suffer fromseveral disadvantages, including the need for an even horizontal airinflow, danger to birds and air traffic, obscuring the landscape withbanks of rotating windmills, and in the case of large diameterhorizontal axis propellers, supersonic speeds at the tips of the rotors.

Vertical axis wind turbines (VAWT) have been provided in the prior artwith a central rotor surrounded by stationary devices that serve toredirect and compress air flow toward the rotor blades.

Compared to VAWT where its exposure remains constant regardless of thewind direction, the horizontal axis windmill must turn to face the winddirection, which is considered a disadvantage as there are additionalmoving parts involved in the construction.

An example of vertical axis wind turbine is shown in U.S. Pat. No.5,391,926 to Staley et al. that uses double curved stator blades todirect wind current to the rotor assembly and to increase structurestability of the thin stator blades.

U.S. Pat. No. 6,015,258 to Taylor discloses another wind turbine thatincludes a ring of stator blades of an airfoil shape to reduce impedanceof air directed towards the central rotor assembly.

Further, U.S. Patent Application Publication No. 2002/0047276 A1 (ELDER)discloses an outer ring of planar stator blades to direct flow of windinto a central rotor assembly.

Canadian Patent No. 1,126,656 (SHARAK) discloses a vertical axis turbinewith stator blades that redirect the air to the rotor blades by straightextending vertical air guide panels that intermittently surround therotor unit and direct air currents to the rotor unit for rotation by thewind. The air guide panels are closed at the top and bottom byhorizontally extending guide panels that are canted in complementarydirections. The upper panel is tilted downwardly as it progressesinwardly and the lower panel is tilted upwardly on its inward extent tothereby increase the velocity and pressure of the wind as it is directedto the rotor unit.

Another Canadian Patent Application No. 2,349,443 (TETRAULT) discloses anew concept of vertical axis wind turbine comprising an air intakemodule, which redirects the airflow vertically to a series of rings withparabolic evacuations. One of the major drawbacks of that design is thefact that the air intake module needs to face the wind, so it requires ayaw mechanism to orient it into the wind. Moreover, the whole designforces the airflow to change its direction from horizontal to verticalinto a sort of internal enclosure from where the air is evacuated bychanging again its direction from vertical to horizontal. The numerousand drastic changes in airflow directions entail a power loss in theairflow and a reduction of the turbine efficiency, as the energy of thewind is transformed into rotation of the turbine only at the lastairflow direction change.

A disadvantage of all the horizontal and vertical axis windmills of theprior art relates to their inability to use remaining energy left in theairflow after hitting the windmill blades. Ideally, the airflow exitinga blade will be reused again and again to a certain extent.Unfortunately, in most cases the prior art enables the capture of only afraction, the first impulse, of the wind power.

A prior art that uses the fluids' properties to transform efficiently alinear fluid movement into a rotational mechanical movement is theturbine described in U.S. Pat. No. 1,061,142 accorded to Nikola Tesla in1913. The Tesla turbine used a plurality of rotating disks enclosedinside a volute casing and the rotation of the turbine was due to aviscous high-pressured fluid, oil in Tesla experiments, directedtangentially to the disks. Unfortunately this previous art is not suitedto capture wind energy for several reasons such as the air viscosity istoo low, the normal wind speed is too low and the whole design with acasing enclosure and only one access opening is impractical for windturbines.

The International Patent Application No. PCT/CA2006/000278, attributedto the applicant, and published under No. WO2006089425A1 discloses awind turbine including a stator assembly having a plurality of statorblades for tangentially redirecting wind into a rotor assembly having aplurality of vertical rotor blades disposed circumferentially on aplurality of disks stacked one on top of each other. The extraction ofthe wind energy using the boundary layer effect, via stacked disks,proves to be very efficient over the portion of the air flow that entersbetween the rotor's disks. However, one of the drawbacks of that designis the fact that the stator assembly, as designed with the stator bladesredirecting the wind tangentially into the rotor, creates around therotor a natural enclosure that prevents the air flow to enter or exiteasily, hence creating a region of high pressure in front of the turbineforcing the majority of the air flow to diverge from its path onto theturbine, which ultimately reduces the wind turbine's total efficiency.

There is therefore a need for a boundary layer stacked disk design thatdoes not need any stator assembly, allowing the airflow to enter andexit freely into and from the rotor assembly.

OBJECTS OF THE INVENTION

It is a preferred object of the present invention to provide a verticalaxis wind turbine boundary layer stacked disk design where the air flowis imparted tangentially to the disks without any need for statorassembly.

It is a further preferred object of the invention to provide a turbineassembly that is structurally reinforced.

It is a further preferred object of the invention to provide a turbineassembly that is simply constructed of inexpensive light material.

It is a further preferred object of the present invention to provide avertical axis wind turbine based on the Coanda effect in fluids whichtranslates into an efficient wind turbine.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a wind turbinecomprising a rotor assembly having a plurality of stacked disks forrotation about an axis, at least one set of the stacked disks havingdisks being closely spaced from each other for creating a boundary layereffect on surfaces of the disks that contributes in rotating the disks,each disk having a plurality of rotor blades disposed on an outercircumference thereof, each rotor having at least one surface extendingtangentially from the outer circumference of each disk so as to redirectthe airflow tangentially to a peripheral surface of each disk, each diskdefining at least one opening thereon for redirecting the wind axiallythrough each of the disks.

Preferably, a wind turbine according to the present invention is able tooperate in very broad wind conditions, such as velocities up to 130 mph(200 Km/h), and frequently changing wind directions. The device providesa reliable and effective means for directing air currents into the rotorassembly, which is attached directly to a vertical shaft.

In general terms, the invention involves various embodiments of avertical-axis wind turbine. Preferably, the rotor blades are designedwith an airfoil profile and disposed tangentially to the disks. Therotor blades are disposed around the circumference of the disks as suchthat, regardless of the wind direction, the air inflow will beredirected tangentially to the disks' surfaces to impart a higherrotational velocity and greater torque upon the turbine shaft. In apreferred embodiment, the rotor blades are angled from the verticaldirection and form a helical shape to allow smooth transitions of theblades over the incoming airflow.

The turbine may be equipped with any number of disks; however apreferred embodiment has at least 50 disks.

In a preferred embodiment, the turbine is designed with an airflowaugmenter stator assembly where the stator blades impart the airflowdirectly into the rotor assembly. The significant size differencebetween the inflow and the outflow openings of the air channels createdby the stator blades create a natural compression and a substantial airspeed increase that achieve higher efficiency even in low wind. Thedisposition of the stator blades also prevents the disruption ofrotation by shielding the rotors from winds counter-directional to theirrotation which may occur as the wind shifts. The stator assembly may beequipped with any number of stator blades; however a preferredembodiment has between six and twelve stator blades.

Preferably, the wind turbine acts to convert wind currents intomechanical energy used to directly act upon a water pump, or to drive anelectrical generator for use as an alternate power source.

The invention as well as its numerous advantages will be betterunderstood by reading of the following non-restrictive description ofpreferred embodiments made in reference to the appending drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a vertical axis wind turbine as seenfrom the exterior, where the airfoil shape and the tangent dispositionof the rotor blades are visible, according to a preferred embodiment ofthe present invention.

FIG. 2 is a top view of a disk presenting the tangent airfoil bladescontinued with the ribs as in FIG. 1.

FIG. 3 is a perspective view of an assembly of ten (10) disks as in FIG.1 providing more details thereof.

FIG. 4 is a perspective view of the turbine with an airflow augmenterstator assembly, according to a preferred embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a vertical axis wind turbine as seen from the exterior,where the airfoil shape and the tangent disposition of the rotor blades2 are visible, according to a preferred embodiment of the presentinvention. The rotor blades 2 redirect the airflow tangentially to thedisk surface 1. The rotor assembly 11 is mountably connected to theshaft 12.

FIG. 2 is a top view of a single internal disk presenting the airfoilblades 2 uniformly distributed on the circumference of the disk. Theupper and lower surface of the disk 1 may be equipped with a certainnumber of ribs 3. In a preferred embodiment, each blade 2 has acorresponding rib on the upper surface and between two blades 2 there isa corresponding rib on the lower surface. The disk 1 may be equippedwith any number of blades 2. However, in a preferred embodiment thenumber of blades 2 is between six (6) and twelve (12). Similar to Tesladisks, each disk may have three arc-sector openings 4 to let the aircirculate between the disks. The ribs 3 are disposed in a spiralarrangement and project from one corresponding rotor blade 2 on thecircumference of the disk 1 to the outer circumference of the openings4.

The airfoil shape of the rotor blades 2 and their tangential dispositionto the disk circumference redirect the airflow tangentially to thesurface of disk. The length of the blade 2 and the number of the bladeson the circumference of the disk are in a close relationship, as suchthat the gap between the tip of a blade 5 and the tail 6 of the nextblade prevents any airflow to travel in a counter-rotating directionbetween the disks 1.

FIG. 3 shows an assembly of ten (10) disks of the wind turbine. Each ofthe rotor blades 2 has a top protrusion 7 for easy assembly into thecorresponding blade of the nearest upper disk in the rotor, which isprovided with a lower recess (not shown). Similarly, the central flange8 of the disk has an annular protrusion 9 that is inserted into thecentral flange of the upper disk. In the final assembly, the pluralityof rotor blades 2 are mounted one on top of the other and create ahelically angled shape as shown in FIG. 1. In addition to providing avery easy assembly method for the rotor assembly 11, the whole structureis well reinforced as each disk 1 is tightly coupled with itscorresponding top and bottom disk on the central flange as well as on aplurality of points uniformly distributed on the circumference.

The illustrated rotor blades orientation is counter clockwise. It willbe understood of course that the orientation of the rotor blades 2 maybe reversed to drive the turbine in a clockwise direction if desired.

A vertical shaft 12 passes through the center of each disk 1. The rotorassembly is preferably manufactured from a corrosion resistant lightmaterial, such as reinforced fiberglass composite, to rotate very easilyeven in slow wind.

The airflow hits with its first impulse the airfoil blades 2 and thenenters in the space between two disks 10 of the rotor assembly 11. Theairflow creates a laminar region on the surface of each disk 1 thatextends up to 0.03 inch (0.762 mm) thick. Doubling that for the twodisks and considering a transition layer, the distance between two disksis best set to be less than 0.1 inches (2.54 mm). However, the turbinerotates in the wind even with wider disk distances. Due to the Coandaeffect, the airflow adheres to the disks surface adding rotationalvelocity to the rotor assembly 11 via the viscous pressure effect. Then,the air passes through the openings 4 of the disks 1 and creates avortex that contributes to increase the rotation of the turbine and as aconsequence its efficiency. The air currents and vortices are able toescape from said enclosure through the openings 4 of the disks 1.

As persons skilled in the art will understand, a majority of the disksmay be closely spaced apart, while some of the disks may be separated bylarger distances. However, the efficiency of the rotor assembly may bediminished with such configuration.

FIG. 4 is a perspective view of the turbine with an airflow augmenterstator assembly 13. The stator blades 14 of the augmenter statorassembly 13 are oriented with a relative small angle from the radialposition in the rotating direction of the rotor, as such to permit theairflow to enter and exit freely into and from the rotor assembly 11. Ina preferred embodiment, the augmenter stator assembly 13 has a top and abottom truncated cones 15 that together with the stator blades 14 createa significant size difference between the inflow and the outflowopenings, which in turn create a natural compression and a substantialair speed increase of the wind, that translates into a steady rotationof the turbine even in low wind. The stator assembly 13 contains a topcover 16 to prevent precipitations to get inside the top cone. Moreover,the top cover 16 redirects the airflow that normally goes over the topof the stator assembly to the back of the turbine where it is attractedtoward the rotor assembly 11 due to a lower pressure region created onthe back of the wind turbine.

Alternatively, the top and bottom surfaces of the stator assembly may behemispheres or elliptical surfaces.

The rotor disks are preferably made from a light non-corrosive material,preferably a light polymer. The stator structure is preferably made froma more resistant non-corrosive material, such as a stronger type ofpolymer. The whole vertical axis turbine may be made from inexpensiveplastic material to create a cost effective alternate power source.

Although the above description relates to a specific preferredembodiment as presently contemplated by the inventor, it will beunderstood that the invention in its broad aspect includes mechanicaland functional equivalents of the elements described herein.

Experimental Tests

A model of the wind turbine was simulated via specialized CFD tool andthen a prototype was built as proof of concept. The prototype included astator assembly. The prototype has one (1) meter in height and 0.70meter in diameter and develops 600 Watts in a wind of 14 m/s.

Without limiting the possibilities of alternate embodiments, there isdescribed below some of such functional equivalents of the boundarylayer vertical axis turbine.

In alternate embodiments of the turbine:

-   -   the turbine may be placed in a horizontal axis position. Such        embodiment may be used in places where the wind is known to have        only one direction or it may be used in a configuration where        the turbine is placed on objects in motion (such as cars, boats,        etc.) to generate the required electrical power;    -   the surfaces of the rotor to create the boundary layer effect        may be designed in different shapes instead of disks;    -   the disk openings may have any shape instead of arc sectors;    -   the rotor may be designed in a shaftless configuration with a        complete circle hole in the middle instead of the arc sector        openings. In this configuration the rotor structure is well        reinforced as each disk is tightly coupled with its        corresponding top and bottom disk on the plurality of points        uniformly distributed on the circumference. The rotor has a top        and bottom shaft portion attached to the corresponding top and        bottom disks, thereby defining a virtual shaft;    -   the disks can be designed without any central openings but with        a radial cut from the central flange to the circumference. The        disk surface is split vertically along the radial cut with the        same disk gap as described in the preferred embodiment. The        rotor assembly of a plurality of such radial cut disks creates a        helical surface which guides the air flow upward or downward        without any need for central openings in the disks. An example        of this feature is shown in FIG. 11 of WO2006089425 (NICA).

Although preferred embodiments of the present invention have beendescribed in detail herein and illustrated in the accompanying drawings,it is to be understood that the invention is not limited to theseprecise embodiments and that various changes and modifications may beeffected therein without departing from the scope or spirit of thepresent invention.

1. A wind turbine comprising: a rotor assembly having a plurality ofstacked disks for rotation about an axis, at least one set of thestacked disks having disks being closely spaced from each other forcreating a boundary layer effect on surfaces of the disks thatcontributes in rotating the disks, the plurality of stacked disks havinga plurality of rotor blades disposed on an outer circumference thereof,each rotor blade having at least one surface extending substantiallytangentially from the outer circumference of each disk for redirectingat least a portion of the wind substantially tangentially to aperipheral surface of each disk.
 2. The wind turbine according to claim1, wherein the rotor assembly is adapted to rotate about a verticalaxis.
 3. The wind turbine according to claim 1, wherein the rotorassembly is adapted to rotate about a horizontal axis.
 4. The windturbine according to claim 1, wherein each of the rotor blades has anairfoil shape placed tangentially to the circumference of each disk. 5.The wind turbine according to claim 1, wherein the length of the rotorblade and the number of the rotor blades on the circumference of thedisk are selected such that the gap between the tip of a blade and thetail of the next blade prevents airflow to travel in a counter-rotatingdirection between the disks.
 6. The wind turbine according toclaim 1,wherein each of the disks has an upper and lower surfaces, at least oneof the surfaces being provided with ribs for redirecting at least aportion of the wind.
 7. The wind turbine according to claim 6, whereineach of the ribs is curved and projects from one corresponding rotorblade to create a spiral-like airflow within each disk.
 8. The windturbine according to claim 6, wherein the rotor blades form a helicalshape.
 9. The wind turbine according to claim 6, wherein between tworibs on one of the surfaces of each disk there is provided acorresponding rib on the other surface of each disk.
 10. The windturbine according to claim 6, wherein each rotor blade of each disk isadapted to be assembled into corresponding rotor blades of adjacentupper and lower disks of the rotor assembly.
 11. The wind turbineaccording to claim 2, wherein a diameter of top and bottom disks islarger than the diameter of intermediate disks.
 12. The wind turbineaccording to claim 2, wherein the rotor assembly is attached via a shaftto an electrical generator.
 13. The wind turbine according to claim 2,wherein each of the disks defines at least one opening positioned near acenter thereof for redirecting at least a portion of the wind axiallythrough each of the disks.
 14. The wind turbine according to claim 2,wherein each of the disks has a helical shape with a radial openingextending from a central flange to a circumference thereof.
 15. The windturbine according to claim 2, further comprising a stator assemblysurrounding the rotor assembly, the stator assembly comprising aplurality of stator blades that impart the airflow into the rotorassembly.
 16. The wind turbine according to claim 15, wherein the statorassembly comprises top and bottom surfaces containing a plurality ofopenings to permit air currents to escape from said rotor assembly. 17.The wind turbine according to claim 16, wherein the top and bottomsurfaces are hemispheres surfaces.
 18. The wind turbine according toclaim 16, wherein the top and bottom surfaces are truncated conessurfaces.
 19. The wind turbine according to claim 16, wherein the topand bottom surfaces are elliptical surfaces.
 20. The wind turbineaccording to claim 1, wherein the rotor assembly includes a shaft andthe stacked disks are mountably connected to the shaft.
 21. The windturbine according to claim 1, wherein the rotor assembly includesportions of the stacked disks that are coupled to one another to definea virtual shaft.